One conventional method for characterizing the features of hydraulic fractures includes hydraulic fracture monitoring (HFM). HFM uses an array of geophones to map microseismic events that occur in the reservoir rock by the creation of a fracture. Oftentimes, however, the acoustic energy created by the rock when it is fractured is too minor to detect, or the acoustic energy is generated by adjacent portions of the rock, rather than the fracture itself, producing inaccurate results.
Increased accuracy can be achieved by introducing explosive pellets into the fracture and monitoring the acoustic energy generated by the pellets when they explode. The pellets are adapted to be heated by the fluid within the reservoir and to detonate at a predetermined temperature. Accordingly, the pellets are designed to detonate at a temperature less than or equal to the reservoir temperature. For shallow reservoirs having a temperature less than about 100° C., the transportation and storage of the pellets can be dangerous, however, because the pellets are designed to detonate at a temperature less than or equal to 100° C. In some climates, such pellets can be exposed to temperatures close to or exceeding 100° C. during transportation and in storage.